We study the molecular genetics of mammalian development. Our interest is focused on developmental controls exerted by LIM-homeodomain (LIM-HD) transcription factors that are encoded by individual members of the Lhx gene family. In the embryo, and also in the adult, Lhx Genes mediate the transit from the stem cell stage to a precursor stage that precedes terminal differentiation. In our earlier experiments, we determined the functions of a number of Lhx genes through loss-of-function analysis of knockout mice, and we described obligatory cofactors, encoded by Ldb and Ssdp genes, respectively, that mediate Lhx gene function. In the work described here, we have adopted regimens of Cre-mediated conditional mutation, originally developed in our laboratory, to ask more fine-tuned questions regarding the action of LIM-HD/cofactor complexes and their downstream Dkk targets as patterns form and organs are established in the developing mouse embryo.